Gaseous diffusion paper deacidification

ABSTRACT

Paper, for example having a pH of about 5.0 or lower, is rendered resistant to the deterioration that is promoted by acidic conditions in paper by impregnating the paper, for example in the form of a book, with gaseous morpholine.

United States Patent [1 1 Kusterer, Jr. et a1.

[ Nov. 13, 1973 1 GASEOUS DIFFUSION PAPER DEACIDIFICATION [75]Inventors: James E. Kusterer, Jr.; Reavis C.

Sprouli, both of Richmond, Va.

[73] Assignee: Research Corporation, New York,

[22] Filed: Dec. 30, 1971 [21] Appi. No.: 214,217

[52] US. Cl 21/58, 21/7, 21/76,

117/154, 252/401 [51] Int. Cl A611 13/00 [58] Field of Search 21/58, 7,76;

[56] References Cited UNITED STATES PATENTS 3,472,611 10/1969 Langweli21/58 2,185,954 1/1940 Ryner 21/58 UX 3,135,627 6/1964 Sadier 117/1433,419,498 12/1968 Paiumbo et a1 162/160 X Primary Examiner-Morris O.Wolk Assistant Examiner-D. G. Miilman Attorney-John W. Behringer et a1.

[57] ABSTRACT Paper, for example having a pH of about 5.0 or lower, isrendered resistant to the deterioration that is promoted by acidicconditions in paper by impregnating the paper, for example in the formof a book, with gaseous morphoiine.

10 Claims, 2 Drawing Figures PATENIED NM 13 I975 FIG].

F/GZ.

GASEOUS DIFFUSION PAPER DEACIDIFICATION This invention relates to aprocess for treating paper to render it resistant to the deteriorationthat is promoted by acidic conditions in paper. More particularly, itconcerns such a process wherein the treatment constitutes impregnatingthe paper with gaseous morpholine.

The recognition of the severe problem of deterioration of documentsprinted on paper that is or becomes acidic has prompted the developmentof several different processes for deacidifying such paper so as to haltor slow its deterioration. Prime examples of acidic papers which aresusceptible to such deterioration (caused by hydrolysis of acidic ionswhich impregnate the cellulose during manufacture) are groundwood (asopposed to chemical wood) papers and alum-rosin sized papers, whethermade of wood or rags. Some of the deacidification processes which haveheretofore been developed are disclosed in "Restoration Methods, by W.J. Barrow, The American Archivist, 6: ll-l54, July 1943;Permanence/Durability of the Book-ll]: Spray Deacidification," publishedby W. J. Barrow Research Laboratory, 1964; "Vapor Phase Deacidification:A New Preservation Method," by Paul McCarthy, The American Archivist,32: 333-342, October i969; and U.S. Pat. No. 3,472,611 to Langwell. Eachof these processes shares at least one common ob jective: to efi'ect along lasting elevation of the pH of the paper. If this is accomplished,then the deterioration of the paper that is induced by acidic conditionstherein will be substantially alleviated.

The paper deacidification processes heretofore developed, however, oftenpossess significant drawbacks. Some, for example those involving aleaf-by-leaf treatment, while perhaps technically effective, areprohibitively expensive. Others, such as ammoniation, may provide only ashort-lived resistance to deterioration. Still other processes may belonger lasting in their intended effect, but have one or moreundesirable side effects, such as causing discoloration, e.g.,yellowing, of the paper, diminution of the papers fold endurance,cockling of the paper, and leaving the paper with a lingering,unpleasant odor. Still other methods of treatment may require the use ofparticularly noxious andlor strongly toxic chemicals (e.g.,cyclohexylamine), thereby requiring relatively elaborate equipment toconduct the treatment safely. There is, then, an urgent need foreffective, safe and relatively inexpensive methods of treating paper soas to render it resistant to acid-catalyzed deterioration. The magnitudeof the problem is revealed, for example, in The Case of the VanishingRecords, by David G. Lowe, American Heritage, volume XX, No. 5 (1969),page 34.

The invention will be understood from the following description, madewith reference to the accompanying drawings. In the drawings:

FIG. 1 is a view, partly broken away, of an apparatus suited for thepractice of the process of the invention; and

FIG. 2 is a horizontal section, taken along line 22 of FIG. 1.

it has now been discovered that paper which is susceptible toacid-catalyzed deterioration can be efi'ectively, safely, and relativelyinexpensively deacidified, and thereby made resistant to suchdeterioration, if it is impregnated with gaseous morpholine. Moreover,it

has been found that such treatment can be effected even with tightlyclosed books, so well will 7.6, penetrate them, and the resultantdeacidification is extremely long lasting, maybe even permanent.

The extent of morpholine impregnation of paper that is to be deacidifiedby the process of the present invention is preferably sufficient toprovide the paper with a pH (measured after the paper has been allowedto stand at room temperature and atmospheric pressure for 24 hours) ofat least about 7.6, preferably at least about 8.5. The pH valuesreferred to are those of the resultant aqueous solution when one gram ofoneeighth inch square pieces of the treated paper is soaked for 1 hourin ml. of distilled, deionized water at room temperature. As determinedby this method, the initial pH value of paper which is susceptible tothe deterioration that is alleviated by the present invention is usuallyabout 5.0 or lower, and frequently about 4.3 or lower.

The time period required to complete such an impregnation process willof course vary, depending upon the amount and type of paper beingtreated, the amount of morpholine employed, the treatment temperature,the pH level desired for the paper, etc. As an example, however, a bookhaving an initial pH of, for instance, about 4.3 can be made to have apH of 8.3 in as little as 8 hours when immersed in an approximately [00percent morpholine atmoshpere at room temperature. No harm to the paperhas been observed to occur through prolonged treatments, but it isgenerally unnecessary to continue the treatment for more than about 4days.

No special treatment temperature is required for the present process;however, preferred operating temperatures are in the range of about 5C.to 128C, most especially about 25C. to C.

The gaseous morpholine used in the present process can, if desired, bein admixture with one or more other gases, such as air, that arenon-interfering with the deacidification process. Preferably, though,the morpholine accounts for at least about one-third, and mostpreferably a major amount, e.g. about to I00 percent, or even 98 to 100percent, of the volume of the atmosphere surrounding the paper duringtreatment.

impregnation of the paper with the gaseous morpholine can be effected bysimply contacting the aper with morpholine vapors. The vapors may beunder atmospheric, sub-atmosphierc or superatmospheric pressure. At roomtemperature the pressure exerted by a 100 percent morpholine atmosphereis about 7 to 10 mm. Hg, which is entirely adequate to penetrate thepaper.

It may be desirable after treating paper according to the presentprocess to pass air over the paper under subatrnospheric pressure so asto permit the escape of any excess morpholine present and thereby lessenthe residual morpholine odor of the .paper.

It has been observed that the treatment of this invention can discolorand/or render tacky any book covers that contain pyroxylin. Such coversshould therefore preferably either be removed or tightly encased in aprotective covering such as polyethylene film prior to treatment of thebook.

It has also been observed that paper treated according to the presentprocess retains its high pH slightly better, and therefore bettermaintains its resistance to deterioration, if it is kept in a dryatmosphere. The

more humid the storage atmosphere, the somewhat poorer will be the pHretention. Nevertheless, the present process is useful even if notfollowed by storage in a dry atmosphere, as evidenced by the fact thateven 6 months storage under I percent relative humidity at 23C. willcause only a modest drop in pH, e.g., from about 8.5 to 7.4 or 7.7.

The invention will be better understood by reference to the followingnon-limiting examples.

EXAMPLE 1 Four sets of experiments were run using the apparatus shown inFIG. 1 of the attached drawings. Referring now to H6. I, there is showna rigid, round containment vessel fitted with a lid 11 that is clampedin place during use by clamps l2 and 13. In the bottom of vessel 10 isan open bowl 14 which contains a much smaller, open dish 15. Resting onthe top of bowl 14 is a horizontal screen 16 which substantially fillsthe cross-sectional area of vessel 10. Mounted to the underside of lid11 is fan blade 17, driven by motor 18. Mounted on top of lid 11 ishandle 19. The diameter of vessel 10 is about inches at its base andabout inches at its top. The height of the vessel is about 26 inches.

The above apparatus is used in practicing the present process by placingliquid morpholine in dish 15, then putting screen 16 in place on top ofbowl 14, and then placing the paper to be treated on top of screen 16.The lid 11 is then clamped into place and fan motor 18 is turned on. Themorpholine then vaporizes and mixes with the air in the vessel andimpregnates the paper.

In each experiment samples of 100 percent chemical wood paper weretreated in the apparatus of FIG. I with gaseous morpholine at roomtemperature. The paper is composed of 49 percent Puget sulphite pulp, 24percent bleached soda pulp, and 27 percent Astracel hardwood pulp, isfilled with bag clay, and is sized with alumrosin. Control samples ofthe paper (untreated) were tested for pH, tear resistance, and foldendurance.

The treatment time in the morpholine-containing vessel was shortenedwith each succeeding set of experiments, as reported hereinafter inTables I, ll and Ill. After treatment, some of the paper samples wereimmediately evaluated for pH, fold endurance, and tear resistance, whilethe remainder were first heat-aged in a dry oven for varying periods atl00C. The pH levels of the treated samples (reported in Table l) weremeasured after each aging period, and the fold endurance and tearresistance values (reported in Tables ll and III) were obtained afterthe 12 day aging period. From the fold endurance and tear resistancevalues were calculated the useful half-lives of the treated anduntreated paper at the dry oven accelerated aging temperature, 100C.These too are reported in Tables ll and III.

Fold endurance testing was performed with The Mars sachusetts Instituteof Technology Folding Endurance Tester which repeatedly bends a 15 mm.wide strip of the paper to be tested across a line in a 270 arc, under Akilogram tension, until failure. The endurance was recorded as theaverage number of bends endured per strip, after testing 50 strips. Bothmachine directional fold endurance (M.D.) and cross directional foldendurance (C.D.) were determined in this manner.

Tear resistance testing was performed with the Elmendorf Tear Tester.

TABLE I pH Length of pll after treatment and aging at 100 C. for thefollowing helore morpholine pH after number of days treattreatment,treatment. Sel. merit hours before aging 2 days 4 days 6 days 8 days 10days 12 (lays 4.3 8 4 8.4 8.8 7.!) 7.8 7.6 7,5 4. 3 8. 6 8. 4 8.] 7. 77. 5 ti. 4 fl. [l 4. 3 8. 7 7 S 7. ll 7. 2 6. l G. 9 ti. 6 4. 3 8. 6 7 76. 8 7.0 5. ti 5. H (i. I)

TABLE It Average told endurance after treatment, bends per strip IAverage [old endurance before treatment or ag- Length of Aftertreatment, After treatment, Hall-life (days) mg, bends per stripmorpholine before aging after 12 days aging at 100 C. treatment, SetMI). 0 D hours M.D. C.D. MD. C.D. M1). (3.1).

397 88 9B 347 El 62 36 4. 6 l0. 7 397 88 48 360 B1 21 3 7 397 88 24 41898 24 26 3 6. 4 397 88 8 352 91 11 i7 2. 4 4. 6 397 88 None 397 88 1D 122. 3 4

Aged but not treated with morpholine.

TABLE III Average tear resistance alter treatment, grams tear Averagetear resistance before treatment. or aging, Length of Alter treatment,After treatment, Hall-lilo (days) grams tear morpholine before agingalter 1'2 days aging at I00" (7. treatment, e hot v1.1) C D hours MI).(3.1). MI). (Ll). MA). (3.1).

5'2. 0 57. z 96 56. 2 60. 1 41. l 43. 8 3D. 2 52. [l 57. .2 4B 53. 2 B2.0 33. 7 40. 0 2t). 4 21 52.1) 57. 2. 24 53. U 65. 0 39. J 48.1) 27 2752.0 57. .2 it 54.1 50.8 34. 38.5 18.7 17.3 52.1) 57. 2 Nom- '5.!. ll57. Z '17.!) 2}. 4 8 7 J. 3

Aged but not treated with morpholine.

The test data in Table 1 illustrate quite clearly the long-lastingquality of the deacidification that is effected by the process of thepresent invention.

The test data in Tables I1 and ill demonstrate that the deacidificationtreatment of the present invention provides resistance to strength lossand a much longer useful life than that to be expected for the untreatedpaper. Thus, for example, the paper that had been treated withmorpholine for 96 hours (i.e., that of set 1), had a fold endurancehalf-life at 100C. of 4.6 days in the machine direction and 10.7 days inthe cross direction, whereas the untreated paper had a half-life underthose conditions of only 2.3 days M.D. and 4 days C.D. Similarly, thetear resistance half-life at 100C. of the paper that was treated withmorpholine for 96 hours was about 30 hours in both directions, while theuntreated papers half-life was only about 9 hours in both directions.

EXAMPLE [I Four more sets of experiments were run, but using a differentapparatus than that depicted in FIG. 1 of the attached drawings. Theessential difference was that the apparatus used for this set ofexperiments was airthis example was considerably greater, due to theremoval of air by the vacuum pump. To prevent morpholine from contactingand possibly harming the pump, a condenser was placed in the linebetween the treatment chamber and the vacuum pump.

in this apparatus and manner, then, samples of the same type of chemicalwood paper used in Example 1 were treated with gaseous morpholine, anduntreated control samples were tested for tear resistance as well as pH.

Again the treatment time was shortened with each succeeding set ofexperiments, as reported hereinafter in Tables 1V, V, and V1. Aftertreatment, some of the paper samples were immediately evaluated for pH,folding endurance, and tear resistance, while the remainder were firstheat-aged in a dry oven for varying periods at 100C. The pH levels ofthe treated samples (reported in Table IV) were measured after eachaging period, and the fold endurance and tear resistance values wereobtained after the 12 day aging period. From the folding endurance andtear resistance values there was calculated for each sample thehalf-lives (both M.D. and CD.) after the 12 day accelerated agingprocess. These percentages are reported in Tables V & V1.

TABLE IV 1V" 4.3 96 9.1 8.9 8.8 8.7 8.5 8.5 8.5 2V" 4.3 48 9.1 8. 5 8.88.3 8. 4 8.5 8. 4 3V 4.3 24 8.9 8.5 8. l 8.4 8.4 8.3 8. .2 4V 4.3 8 9.08. 5 8. 5 8.3 7. 4 7.8 8. 0

"V=Treated in vacuum chamber.

TABLE V Average 101d endurance Average told endurance after treatment,bends per strip before treatment or ag- Length of After treatment Aftertreatment, Half-life (days) ing, bends per strip morpholine before agingafter 12 days aging at 100 C.

res ment Set MJ) C.D. hours M.D. C.D. M.D. C.D. M.D. (1.1).

397 88 96 136 19 16 4. 5 1(1 397 88 48 143 44 20 16 4. 7 $1 397 88 24171 49 2B 20 5 10. 3 397 88 B 154 54 23 Z] 4. 3 R. 7 397 88 None 397 '8810 12 2. 3 4

Aged but not treated with morpholine. "V=Ireated in vacuum chamber.

TABLE VI Average tear resistance after treatment, grams tear Averagetear resistance before treatment or Length of After treatment, Aftertreatment, Half-life (days) aging, grams tear morpholine before agingalter 12 days aging at 100 C. treatment, W Set M.D C.D. hours M.D. O.D.M.D. C.D. M.D. CD

52. 0 57. 2 96 56. 8 64. 0 37. 9 43. 6 23. 4 27 52. 0 57. 2 48 56. 0 60.4 41. 8 47. 2 33. 7 35 52. 0 57. 2 24 53. 3 60. l) 40. l 47. 0 3'2 34. 352. 0 57. 2 8 54. 7 62. 5 40. 8 47. 4 25. 7 28 Control 52. 0 57. 2 None'52. 0 '57. 2 '17. El 21. 4 8. 7 9. 3

'Aged but not treated with morpholine. =Treated in vaceum chamber.

tight and attached to a vacuum pump. in each of the present experiments,then, the impregnation chamber was placed under a partial vacuum,measuring about 30 inches of mercury. Thus, as compared to theexperiments of Example 1, the morpholine concentration in the gaseousatmosphere around the paper treated in The test data in Table IV againillustrate quite clearly the long-lasting quality of the deacidificationthat is effected by the process of the present'lnvention. Also, thevalues indicate that higher pH values are obtained by using a moreconcentrated morpholine atmosphere in treating the paper than that usedin Example I.

It was also noted, but not reported in Table N, that a decrease in thepH of the treated paper is generally effected by extensive handling ofthe paper, as, for example, in testing it for tear resistance. This pHdepression is generally slight, however. In the case of the samplesreported on in Table IV, for instance, the pH of the paper after agingand testing was usually at least 8.0 and was always at least 7.5.

The test data reported in Tables V and V] again show quite clearly thatthe morpholine treatment of the present invention enables the paper towithstand much better the accelerated aging process, insofar as thepapers tear resistance and folding endurance properties are concerned,than if the paper were not so treated.

As indicated above, the process of this invention is applicable to anypaper that is subject to deterioration due to acidic conditions in thepaper. Thus, the paper can be manufactured from, for instance, sisal,jute, flax, wood, cotton, or any combination of the foregoing. Otherexperiments have been run, for instance, with a paper composed of 50percent cotton linter and 50 percent chemical wood furnish which had apH of about 4.7. impregnation with gaseous morpholine raised that pH toabout 8.6, and the paper retained its basicity and physical propertiesas in the case of the 100 percent chemical wood paper.

We claim:

1. A process for treating paper to render it resistant to thedeterioration that is promoted by acidic conditions in paper, whichprocess comprises impregnating the paper with a gaseous atmosphereconsisting essentially of morpholine, the said morpholine being presentin at least about one-third the volume of the said gaseous atmosphere.

2. The process of claim 1 wherein the paper is in the form of a book.

3. The process of claim 1 wherein the morpholine accounts for about 90to 100 volume percent of the atmosphere surrounding the paper during theimpregnation.

4. The process of claim 3 wherein the paper is in the form of a book.

5. The process of claim 1 wherein the amount of morpholine impregnatedinto the paper is sufficient to provide the paper with a pH (measuredafter the paper has been allowed to stand at room temperature andatmospheric pressure for 24 hours) of at least about 7.6, as determinedby soaking one gram of one-eighth inch squares of the paper for one hourin ml. of distilled, deionized water at room temperature and thenmeasuring the pH of the resultant aqueous solution.

6. The process of claim 5 wherein the paper is in the form of a book.

7. The process of claim 5 wherein the paper prior to treatment has a pHof about 5.0 or lower.

8. The process of claim 7 wherein the paper is in the form of a book.

9. A process of treating a book made of paper having a pH of about 5.0or lower so as to render the paper resistant to the deterioration thatis promoted by acidic conditions, which process comprises impregnatingthe book with a gaseous atmosphere consisting essentially of morpholine,the said morpholine being present in at least about one-third the volumeof said gaseous atmosphere, at about 25 to C. in an amount sufficient toraise the pH of the paper to at least about 8.5, said pH values being asdetermined by soaking one gram of one-eighth inch squares of the paperfor one hour in 70 ml. of distilled, deionized water at room temperatureand then measuring the pH of the resultant aqueous solution.

10. The process of claim 9 wherein the morpholine accounts for about tovolume percent of the atmosphere surrounding the book during theimpregnatlon.

t I i U UNIT D STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,77 ,95 Dated November 3, 973

InVentOI-(S) James E. Kusterer, Jr., and Reavis C. Sproull It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 2, "7.6, should read --the morpholine--:

'line 46, "aper" should read --paper--;

line +8, "sub-atmosphierc should read --subatmospheric--. Columns 3 and4, Table III. fifth column, "53.0" should read --5 I.O--. Columns 5 and6, Table IV should have column headings so as to read as follows:

new

'pH Before I length 0! pH After Treatment, pH After Treatment and Aging100 C}. for the Set Treatment Morphollne Before Aging fiollowlng numberof days Treatment 2 days 4 days 6 days 8 days 10 days 12 days 1 V" 4.3hours 9.1 8.9 8.8 8.7 8.5 8.5 8.5

a v 4.3 48 hours 7 9.1 8.5 8.8 8.3 8.4 8.5 Y 8.4

a v 4.3 24 hours 8.9 8.5 8.1 8.4 8.4 8.3 8.2

4 V" 4.3 8 hours 9.0 8.6 8.5 8.3 "7.4 7.8 8.0

Treated invacuum chamber Signed and sealed this 2nd day of April 1971;.

(SEAL) Attest:

EDWARD M.FIETCHER,JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-l050 (IO-69) USCOMM-DC 60376-P69 U.S. GOVERNMENTPRINTING OFFICE I989 O'366-8J4.

Patent No. 3577 895 Dated November 35 973 In e t James E. Kusterer, Jr.,and Reavis C. Sproull It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2,1 line 2, "7.6, should read --the morpholine-:

"line '46, "aper" should read --p-aper--;

line 48, "sub-atmosphierc" should read --subatmospheric--. Columns 3 and4, .Table III. fifth column, "53.0" should 7 read --5 +.0- I Columns 5and 6, Table IV should have column headings so 1 as to read as follows:

pH Before Length of pH After Treatment, pH Mme; "Treatment 'and Aging100 C. for the Set Treatment Morphollne Before Aging iollowing number ofdays Treatment 2 days 4 days 6 days 8 bye 10 days 12 days 1v" 4.3 95mm9.1 8.9 8.8 8.7 8.5 I 8.5 8.5

1v 4.3 48 hour! 8.1 v 8.5 8.8 8.3 8.4 8.5 8.4 3 4,3 24 hours 8.9 8.5 8.18.4 8.4 8.3 8.2

4V" 4.3 Shouts 9.0 I 8.6 I 8.5 8.3 "7.4 7.8 8.0

" .ITIGIIBG in vacuum: 'chamber Signed and sealed this 2nd day of April1978.:

(SEAL) Attest: I

EDWARD M.FIETCHER,JR. c. MARSHALL DANN Attest'ing Officer Commissionerof Patents U.S. GOVERNMENT PRINTING OFFICE l9, 0-30-834.

FORM Po-1o5o (10-69) USCOMWDC x Patent No.

Inventor(s) Dated November 13, 1973 James E. Kusterer, Jr., and ReavisC. Sproull It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 2, "7.6, should read --the morpholine--:

line 46, "aper" should read --paper-; line 48, "sub-atmosphierc" shouldread --subatmospheric".

Columns 3 and 4, Table III, fifth column, "53.0" should read 54.0".

Columns 5 and 6, Table IV should have column headings so as to read asfollows:

Table IV pH Before length 0! pH After Treatment, pH After Treatment andAging 100' C. to; the Set Treatment Morpholme Beflore Aging followingnumber of days Treatment 2 dayl 4 days 6 days 8 days 10 days 12 days IV"4.3 96hourl 9.1 8.9 8.8 8.7 8.5 8.5 8.5

i V" 4.3 48 houtl 9.1 8.5 8.8 8.3 8.4 8.5 8.4

3 V" 4.3 24 hour! 8.9 8.5 8.1 8.4 8.4 8.3 8.2

4V" 4.3 Bhourl 9.0 8.6 8.5 8.3 7.4 7.8 8.0

" I Tuned in vacuum chamber Signed and sealed this 2nd (SEAL) Attest:

EDWARD M.FIETCHER,JR. Attesting Officer II PO-IDSO (10-69) day of April1971+.

USCOMM'DC 5376-P59 1! [1.5. GOVIHNIENT HIIIIIIIG OIIICE llll 0-588-314.

2. The process of claim 1 wherein the paper is in the form of a book. 3.The process of claim 1 wherein the morpholine accounts for about 90 to100 volume percent of the atmosphere surrounding the paper during theimpregnation.
 4. The process of claim 3 wherein the paper is in the formof a book.
 5. The process of claim 1 wherein the amount of morpholineimpregnated into the paper is sufficient to provide the paper with a pH(measured after the paper has been allowed to stand at room temperatureand atmospheric pressure for 24 hours) of at least about 7.6, asdetermined by soaking one gram of one-eighth inch squares of the paperfor one hour in 70 ml. of distilled, deionized water at room temperatureand then measuring the pH of the resultant aqueous solution.
 6. Theprocess of claim 5 wherein the paper is in the form of a book.
 7. Theprocess of claim 5 wherein the paper prior to treatment has a pH ofabout 5.0 or lower.
 8. The process of claim 7 wherein the paper is inthe form of a book.
 9. A process of treating a book made of paper havinga pH of about 5.0 or lower so as to render the paper resistant to thedeterioration that is promoted by acidic conditions, which processcomprises impregnating the book with a gaseous atmosphere consistingessentially of morpholine, the said morpholine being present in at leastabout one-third the volume of said gaseous atmosphere, at about 25* to75*C. in an amount sufficient to raise the pH of the paper to at leastabout 8.5, said pH values being as determined by soaking one gram ofone-eighth inch squares of the paper for one hour in 70 ml. ofdistilled, deionized water at room temperature and then measuring the pHof the resultant aqueous solution.
 10. The process of claim 9 whereinthe morpholine accounts for about 90 to 100 volume percent of theatmosphere surrounding the book during the impregnation.